Spring-loaded hammer

ABSTRACT

A spring-loaded hammer or percussion drill with a mechanical vibratory system having vibratory masses and springs for cushioning the masses and transmission means so that part of the energy of vibration is transferred in impact form to a percussive tool.

Umted States Patent [151 3, Hoeffleur [451 Aug. 8, 1972 SPRING-LOADEDHAMMER [56] References Cited [72] Inventor: Albert Hoelfleur, Kusnacht,Zurich, UNITED STATES PATENTS swtzeland 2,545,245 3/1951 Stutz ..173/49[73] Assignee: Regus A.G., Zurich, Switzerland 3,291,224 12/1966 Stutz..173/49 [221 Filed Primary Examiner-Ernest R. Purser [21] AppL 52 202AttorneyWatson, Cole, Grindle & Watson [57] ABSTRACT [52] U.S.C1..l73/49 74/61 1 A spring-loaded hammer or percussion dnll wlth a 51Int. Cl ..B2Sd 11/06, Fl6h 33/18 mechanical vibratory system havingvibratory masses of and springs for cushioning the masses andtransmission means so that part of the energy of vibration istransferred in impact form to a percussive tool.

SChinuJDrawingflgures SPRING-LOADED HAMMER The invention relates to aspring-loaded hammer or percussive drill with a mechanical vibratorysystem comprising one or more vibratory masses and several componentsprings for cushioning the vibratory masses against fixed bearingmembers mounted within the hammer casing, and with means whereby thevibratory masses can be caused to vibrate, as well as means oftransmission whereby, at every vibration of those masses, part of theenergy of vibration is transferred in impact form to a percussive toolbit in such a way that the lines of application of the spring actionproduced by the component springs, of the oscillatory displacement ofthe center of gravity of the vibratory masses, and of the force vectorof the impact transmitted to the bit at every vibration, lie in theproduced longitudinal center line of the bit, while that side of thevibratory masses which faces away from the said means of transmissionbears against at least one main spring, at least one buffer spring beingprovided on that side of the vibratory masses which faces towards thesaid means of transmission.

Spring-loaded hammers of that type have long been in existence. in suchhammers, as a rule, the means whereby, at every vibration of the masses,part of the energy of vibration is transferred in impact form to thetool bit consists of a transmission pin in axial alignment with the bit,one end of the pin being in contact with the end of the tool bit shank,while the other end of the pin receives the impact of the vibratorymasses at every vibration, that is to say whenever the vibratory massfollows the rise of the oscillation half-wave, during which the mass maybe regarded as carrying out an excursion from a position of rest towardsthe transmission pm.

Energy of vibration is withdrawn from the mass by the impact, amountingat its maximum to the whole of the kinetic energy possessed by the massat the moment when it strikes the transmission pin. The maximum impactenergy that can be transferred to the transmission pin varies accordingto the particular point to which one adjusts the moment of impact of themass on that pin, in the said rise of the half-wave of the vibrationalmovement of the mass towards the pin.

Consequently, assuming a particular impact energy to be required, eitherone can work with a relatively large mass and/or with a very high energyof vibration in the mechanical vibratory system already mentioned, themoment of impact of the mass on the transmission pin being set in thevicinity of the maximum for free vibration of the mass, or one can use aconsiderably smaller mass and/or a mechanical vibratory system with afar lower energy of vibration, the moment of impact of the mass on thetransmission pin being then set more in the lower part of the rise ofthe free vibration half-wave approaching the transmission pin. In theformer case, the maximum impact energy is small compared to the energyof vibration of the mechanical vibratory system, and the interferencewith free vibration caused by the blows of the mass on the transmissionpin is accordingly fairly small. This solution thus offers theconsiderable advantage of there being little or no interference with thevibration of the mass, but it suffers the great drawback that themechanical complication and expense of the vibratory system arerelatively high, as is also its weight, in addition to which thebuild-up time of the mechanical vibratory system, and hence the timeelapsing from the moment of switch-on of the hammer to that of usefulperformance, is comparatively long. In the latter case, that is to saywhen the moment of impact lies in the lower part of the rise alreadymentioned, the maximum impact energy al' ready constitutes a fairly highproportion of the energy of vibration of the resonant circuit and mayeven equal the energy of free vibration in the event of the moment ofimpact being set at the start of the said rise, that is to say at thezero transition point of free vibration. Now, if precisely the sameimpact energy were transferred from the mechanical vibratory system tothe transmission pin at each blow, then, even with the moment of impactin such a position in the said rise, quasi-stationary, that is to saycyclically repeated, vibration would arise in the mechanical vibratorysystem. This, however, would not be simply sinusoidal, but would beoverlaid by harmonics, with a fundamental frequency governed not only bymass and by the spring characteristic of the mechanical vibratorysystem, but also by the impact energy transferred to the transmissionpin at everyblow. Since, however, the impact energy transferred to thetransmission pin at every blow differs in practice according to theworking conditions encountered by the percussive bit at the point whereit is being used, there will arise in practice, when the moment ofimpact lies in the lower part of the said rise, irregular vibration ofthe mechanical vibratory system, in which a great deal of the power fedby the drive to the mechanical vibratory system will be wasted withinthe vibratory system itself, so that the power available for transfer tothe bit will be reduced accordingly. Furthermore, the sequence of blowswill be irregular or their frequency will be subject to wide variation.

It was to remedy this that is to say to ensure a fairly constantfrequency of percussion and a vibration that is repeated to some extentcyclically in the mechanical vibratory system, without having totolerate the extra technical problems and expense entailed by asubstantial increase in the vibrational energy of the mechanicalvibratory system and/or a substantial enlargement of mass and theraising of the spring characteristic of the mechanical vibratory systemthat the buffer spring mentioned earlier was provided on that side ofthe vibratory mass which lies towards the transmission pin. The effectof such a buffer spring is substantially that it keeps more or lessconstant the energy that is transferred, to the transmission pin andbuffer spring combined, by the vibrating mass as it strikes thebuiferspring and transmission pin. In order words, when the impact energytransferred to the transmission pin is small (When, for example, theobject being attacked offers little resistance to the bit), the bufferspring absorbs the unused impact energy" and returns it to themechanical vibratory system; and when the impact energy transferred tothe transmission pin is great (that is to say when the object beingattacked offers great resistance to the bit), the buffer spring is notcompressed and therefore absorbs no energy. At the same time, because ofthe great resistance offered to the bit by the object under attack, aconsiderable proportion of the impact energy transferred to thetransmission pin is reflected at the object under attack and thenlikewise fed back once more through the transmission pin to themechanical vibratory system. The effect produced by the buffer spring isthus approximately the same, both when the object being attacked is softand when it is hard, namely that, out of the total energy transferred bythe vibrating mass to the transmission pin and buffer spring upon impactwith them, any part that cannot be transferred to the object underattack is conveyed back again to the mechanical vibratory system. Whatis also achieved by the buffer spring is that the energy transferredfrom the vibrating mass to the transmission pin and buffer springremains substantially constant, irrespective of the consistency of theobject under attack, thereby producing the conditions already mentioned,namely constancy of impact energy at every blow and hence alsoperiodicity in the vibration of the mechanical vibratory system.

This vibration, however, as has likewise been mentioned already, isoverlaid to a considerable extent by harmonics. It is only, that is tosay, a quasi-stationary vibration imposed by the drive, and by no meansa pure resonance vibration. The harmonics included in this vibration arenaturally also communicated to the main spring that has been mentioned,against which that side of the vibrating mass which faces away from themeans of transmission is brought to bear. The result is that the mainspring vibrates not only to the fundamental frequency, but also to theharmonics, which in many cases lead to quite considerable energy lossesor the loss of considerable proportions of the energy of vibration.These energy losses in turn result in a reduction in the amplitude ofvibration, that is to say a shortening of the travel of the vibratingmass. That is probably also the reason why spring-loaded hammers,despite the improved working obtainable by the use of such buffersprings, are seldom used in practice, because the said hannonics in thevibration of the main spring make themselves undesirably noticeable inthe form of energy losses and in certain other important respects.

The problem which the invention sets out to solve is therefore toeliminate the difi'rculties arising from harmonics in the main springsof hammers of the type referred to in the preamble and to provide aspringloaded hammer in which the reduction in performance due toharmonics in the vibration of the main spring is either non-existent orgreatly reduced.

This the invention achieves, in a spring-loaded hammer of the type inquestion, by virtue of the fact that the characteristics of the mainspring at particular points along its length differ from the springcharacteristics elsewhere along its length.

In one recommended form of hammer embodying this principle, the mainspring is divided. For this purpose, the main spring may be divided intoseveral preferably two equal lengths.

When the main spring is divided, it is also of advantage for thecharacteristics of the main spring or the parts thereof to be the same,or at least approximately the same, as those of the buffer spring. Inthat case, two or three springs, as desired, identical to the bufferspring, can be used one above the other as the main spring, this havingthe further advantage, as regards manufacture, that springs of only onekind are needed for such a hammer.

The individual parts of the main spring may be linked together bycollars.

Another possible way of providing the main spring with characteristicswhich differ at individual points along its length is to provide themain spring with nonspringy turns, preferably at one or two points bywhich the spring is divided into equal lengths.

The invention is described hereunder with the aid of the accompanyingdrawing of an example embodying the principle thereof wherein:

FIG. 1 is a longitudinal section of a spring hammer in accordance withthe present invention; and

F IG. 2 is a view of a pair of abutting main spring sections, taken atline I and typical for that also taken at line II, slightly enlarged.

As to details, this hammer has four vibratory masses, mountedeccentrically, in pairs of equal eccentricity, on a common shaft, therebeing two outer vibratory masses on the ends of a central shaft and twoinner vibratory masses on a hollow shaft surrounding the central shaft.The two shafts are driven round in opposite directions, at the samespeed, by a common bevel pinion acting on two bevel wheels, the teeth ofwhich face towards each other. The eccentricity of the masses inrelation to one another is such that the inertial forces of theeccentrically mounted masses are superimposed on one another in thelongitudinal direction of the hammer and cancel one another out in thetransverse direction. One of the outer vibratory masses, 1, the innershaft 2 and the rear side of one of the bevel wheels, 3, are shown inthe drawing. The inner shaft 2 is mounted in a vibration block, 4, whichis free to move longitudinally, guided by the guide rods 5. The hollowshaft already referred to is mounted on the inner shaft 2. The bevelpinion already mentioned, for driving the two bevel wheels, is driven bythe electric motor 6 through a safety friction clutch, 7. As will beobserved, the motor 6 is housed in the top of the hammer and secured tothe hammer casing by bolts, 8. Current is supplied to it by the supplylead 9 and switch 10. The top of the hammer also carries two hand-grips,11, for holding the hammer. The vibration block 4, with the fourvibratory masses such as l, bears, through the agency of the three-partmain spring 12a/12b/12c, against part 13 of the hammer casing. The mainspring l2a/l2bl2c, and the vibratory mass formed by the vibration block4 plus its four rotating masses and all other parts rigidly connected tothe vibration block, represent the two energy-storing elements of themechanical vibratory system mentioned previously. At every vibration,the vibration block 4 strikes the transmission pin 14 and the bufferspring 15 and transfers partly to the transmission pin 14 and partly tothe buffer spring 15 a percussive energy approximately equal to thekinetic energy of the vibration block 4 at the moment of impact. Thatportion of this percussive energy which is imparted to the transmissionpin 14 is passed on to the percussion bit 16 and thence to the objectunder attack, by which it is either entirely absorbed (in the case ofsoft or tenacious material, for example) or only partially absorbed andpartially reflected (in the case of hard material), in which latterevent the reflected energy is transmitted back through the percussionbit 16 and transmission pin 14 to the vibration block 4. The percussionbit 16 has freedom of longitudinal motion within the holder 17 and hasonly the end of its shank bearing against the transmission pin 14. Toprevent the bit from falling out of the holder, the latter contains asliding pin that can be held fast by a screw, 18, and the bit is slottedaccordingly at 19. Removal of this securing pin enables the bit to bechanged.

In the present example, the main spring IZa-c is composed of threesprings, each identical to the buffer spring 15, which are fitted oneabove the other. Hence, the main spring l2a-c has one point, I, wherethe springs 12a and 12b are in contact, and another point, II, where thesprings 12b and 12c are in contact, at which its spring characteristicsdiffer from those of the individual springs 12a, 12b and 12c. At thosepoints I and II, only longitudinal compressive forces, i.e. compressiveforces in the direction of the longitudinal center line of the springs,are transmitted, but no longitudinal tractive force or, more especially,torque or forces acting transversely to the longitudinal center line.

In FIG. 2, it can be clearly seen that portions of both springs 12a and12b are flattened so as to flatly abut against one another at line I. Itshould be noted also, that springs 12b and 12c are similarly flattenedso as to flatly abut against one another at line II, as seen in FIG.

The development of harmonics, which tend to be generated in the mainspring by reason of the harmonies overlying the motion of the vibratorymass, is thereby largely prevented. At all events, energy-wastingself-generated resonant responses in the main spring are as good asnon-existent or, if they do arise, are in any case greatly reduced.Other forms of deviation in the characteristics of the main spring, suchas, for instance, the incorporation of non-springy turns, will serve thesame purpose as the use of a divided spring. Non-springy turns, ofcourse, are not altogether comparable to separation points, because thephysical action of non-springy turns differs from that of separationpoints; non-springy turns should be regarded, rather, as interpolatedmasses capable of transmitting only longitudinal forces.

The particular advantage of using a main spring l2a-c made up of several(in the present case, for example, three) part springs similar to thebuffer spring 15 is that the spring characteristic of the individualparts of the main spring is then equal to that of the buffer spring, thedesirable outcome of this being that the harmonic component of themotion of the vibratory mass is kept small. This in turn means that themagnitudes tending to generate natural vibrations in the spring aresmall from the outset, which places a further obstacle in the way of thestimulation of resonant responses in the main spring.

Because of the complexity of the subject and owing to considerabledifiiculties concerned with measurement technique, it has not beenpossible to determine with any certainty what are the physical effectsresponsible for the fact that the natural vibrations of the main springare considerably reduced or almost entirely prevented by the widelyvarying changes in the spring characteristics at particular points. Theforegoing explanations can therefore serve only to demonstrate theproblem and no claim can be laid to completeness or to correctinterpretation of the observed effects. At all events, a distinctmoderation was observed in the type and development of the main springvibrations when the main springs used had discontinuities in theirspring characteristics at particular points. The effect was even moremarked when springs identical to those used for the buffer 15 wereemployed as sections of the main spring.

As to the size of the buffer spring 15, it remains to add that this mustbe able, within its compressibility range, that is to say within itsmaximum travel as a spring, to absorb the entire kinetic energy of thevibratory mass at the moment of impact, as well as the potential energyrepresented by the force of gravity acting on the vibratory mass. Inabsorbing this total energy, the buffer spring should not require tocarry out more than a part of its maximum travel, rather than the wholeor nearly the whole of it. In the present instance, the size of thebuffer spring affects more than the action of the buffer spring as such,in that the main spring, too, is composed of springs identical to thebuffer spring.

In addition to the example shown in the drawing, with three springsidentical to the buffer spring serving as the main spring, a main springmade up of two springs identical to the buffer spring has been tried andfound highly satisfactory. Here again, the conditions, as far as theycould be observed, were much the same as with the example illustrated.

Finally, it is worth mentioning that when collars, such as 21, arefitted at the junction between the individual springs 12a, 12b and 12b,12c composing the main spring, in order to exclude the possibility ofthe individual springs moving sideways in relation to the commonlongitudinal center line, this has no observable adverse action on theadvantageous effect of subdividing the main spring. The distinctmoderation in the type and development of the main spring vibrations,already referred to, could still be seen to be unchanged after thefitting of such collars. It should be stated, however, that the collarswere very light, consisting substantially of no more than a shortsection of tubing having a short flange-like peripheral protruberance inthe middle, between the tube ends as clearly shown in FIG. 2.

What I claim is:

l. A spring-loaded hammer or percussive drill with a mechanicalvibratory system comprising one or more vibratory masses l) and severalcomponent springs including a main spring and a buffer spring (Ila-c and15) for cushioning the vibratory masses against fixed bearing members(13) mounted within the hammer casing, and with means (6 and 7) wherebythe vibratory masses can be caused to vibrate, as well as means oftransmission (14) whereby, at every vibration of those masses, part ofthe energy of vibration is transferred in impact form to a percussivetool bit (16) in such a way that the times of application of the springaction produced by the component springs, of the oscillatorydisplacement of the center of gravity of the vibratory masses, and ofthe force vector of the impact transmitted to the bit at everyvibration, lie in the produced longitudinal center line of the bit,while that side of the vibratory masses which faces away from said meansof transmission bears against said main spring (IZa-c), said bufferspring (15 being provided on that side of the vibratory masses whichfaces towards the said means of transmission; characterized in that saidmain spring, at particular points (I and II) along its length,

has different spring characteristics from those which apply elsewherealong its length, said main spring being divided at such particularpoints.

2. A spring hammer as claimed in claim 1, in which the spring constantof the individual parts (12a, 12b

and 12c) of said main spring is substantially the same as that of saidbuffer spring (15).

3. A spring hammer as claimed in claim 1, in which said divided mainspring is linked together by collars.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 682,254 Dated August 8, 1972 1n\entor(s) Albert Hoeffleur It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the title page, please insert claims priority of Swiss applicationNo. 10531/69, filed July 10, 1969 Signcd and sealed this 20th day ofFebruary 1973.

{SLAM Arrest:

ROBERT GOTTSCHALK Attcstjing l fficor

1. A spring-loaded hammer or percussive drill with a mechanicalvibratory system comprising one or more vibratory masses (1) and severalcomponent springs including a main spring and a buffer spring (12a-c and15) for cushioning the vibratory masses against fixed bearing members(13) mounted within the hammer casing, and with means (6 and 7) wherebythe vibratory masses can be caused to vibrate, as well as means oftransmission (14) whereby, at every vibration of those masses, part ofthe energy of vibration is transferred in impact form to a percussivetool bit (16) in such a way that the times of application of the springaction produced by the component springs, of the oscillatorydisplacement of the center of gravity of the vibratory masses, and ofthe force vector of the impact transmitted to the bit at everyvibration, lie in the produced longitudinal center line of the bit,while that side of the vibratory masses which faces away from said meansof transmission bears against said main spring (12a-c), said bufferspring (15) being provided on that side of the vibratory masses whichfaces towards the said means of transmission; characterized in that saidmain spring, at particular points (I and II) along its length, hasdifferent spring characteristics from those which apply elsewhere alongits length, said main spring being divided at such particular points. 2.A spring hammer as claimed in claim 1, in which the spring constant ofthe individual parts (12a, 12b and 12c) of said main spring issubstantially the same as that of said buffer spring (15).
 3. A springhammer as claimed in claim 1, in which said divided main spring islinked together by collars.
 4. A spring hammer as claimed in claim 1, inwhich said main spring is divided into at least two equal lengths (12a,12b or 12c).
 5. A spring hammer as claimed in claim 4, in which said atleast two springs (12a, 12b or 12c) are identical to said buffer spring(15) and are fitted one about the other, to serve as said main spring(12a-c).